Metabolism is a word that is heard by everyone who is losing weight. It is believed that it needs to be “overclocked” at full capacity, and then you will be able to deceive the body and burn more calories in the same time. Almost like a secret button to press. That’s why metabolism-boosting foods, diets and workouts are so attractive. Read in this article about what metabolism is in general and why it is fast and slow.
What is metabolism?
Evolutionarily, the human body strives to maintain the ideal weight and fat percentage from the point of view of survival, which is set by genetics. This protects a person from any extremes: both from exhaustion and from obesity. Both reduce the chances of passing on their genes to offspring in the wild.
The “ideal” weight for survival is controlled by a part of the brain — the hypothalamus. It is he who slows down or accelerates the metabolism if he sees any deviations from the norm for a particular person. With the help of a variety of substances — hormones, glucose levels and amino acids in the blood, and much more — he collects information about what is happening in the body: is there enough fat stored, does food arrive regularly, how high in calories it is.
Comparing the data with the “ideal” genetic setup, the hypothalamus twists the metabolism up and down, depending on the situation. Let’s look at examples of what an ideal metabolism looks like.
If a person has eaten unusually much for himself for one or several days, his appetite itself decreases in the following days. A person will eat less without noticing it. At the same time, he will be more mobile and active. And even if he does gain extra weight over the holidays or holidays, he will quickly get rid of it as soon as he returns to normal life, without doing anything special for weight loss. The hypothalamus will adjust appetite and activity levels so as to bring the system back into balance.
And the reverse situation. The same person suddenly began to eat unusually little for himself: he went on a diet, stopped eating because of stress, employment. In response to this, the hypothalamus increases appetite in the following days in order to make up for the average calorie content. At the same time, it reduces activity — a person becomes more sluggish, sleepy, moves less and wants to sit or lie down at the first opportunity.
It turns out that a person with a healthy metabolism can have about the same weight for many years without doing anything special.
How does the hypothalamus do this?
The brain controls appetite using a variety of mechanisms.
- Appetite is reduced by leptin, glucagon, obestatin, neuropeptides S and FF, cholecystokinin, neurotensin, enterostatin, thyrooliberin and other hormones.
- Amino acids and glucose in the blood are a sign that a person has eaten.
- A full stomach: it has sensors for mechanical stretching. They tell the hypothalamus about the food inside.
- Reduction of the gallbladder and its production of bile after eating.
- Filling of the intestine.
The following chemicals increase hunger and push a person to search for food and cravings for certain foods, especially high-calorie ones: ghrelin, neuropeptide Y, orexin, galanine, noniceptin, motilin, B-endorphins, etc. As well as low levels of glucose and amino acids, an empty stomach.
A person begins to get more pleasure from food — from its taste, smell. Food becomes a source of pleasure. Dopamine and endorphins are responsible for this, which are released every time a person eats.
This is an excellent defense mechanism against starvation and exhaustion: if we were indifferent to food and not motivated to look for it, we could not get almost narcotic pleasure from it, things with survival would be bad. Although, today it plays against us: there is no need to look for food anymore. The most delicious, fatty and sweet food is in abundance at arm’s length. Because of this, dopamine and endorphin receptors are bombarded more often, stronger and more than nature intended. This knocks down all the internal settings of the body in terms of eating behavior.
Fast and slow metabolism
The metabolic situation described above is ideal. In life, sometimes everything seems to be the opposite: the more a person eats and moves less, the less they want to move and eat more. And someone is thin, eats very little and can’t eat anymore.
To understand about fast and slow metabolism, you need to know this. The human nervous system consists of two departments. The first is the central nervous system. It consists of the brain and spinal cord. The second is the autonomic nervous system. It is the main regulator of metabolism. It controls the work of glands, organs, digestion, manages the nutrients received with food, and does other important things for life.
The autonomic nervous system has two branches: sympathetic and parasympathetic.
- The sympathetic nervous system is activated in life during mental or physical stress, and in the wild – during flight, defense or attack. It “accelerates” metabolism, is responsible for the mobilization of energy from reserves and its use. It controls the work of the muscles, heart, thyroid gland, reproductive system, stimulates the release of adrenaline.
- The parasympathetic nervous system restores the body after stress. It “slows down” metabolism, stimulates digestion, accelerates the absorption of nutrients and their storage. It also controls the immune system.
Depending on the situation – stress or recovery – either one or the other branch is activated for any person. But for some people, each of them can dominate most of the time. This determines the metabolic rate.
It is important to understand: speaking about fast and slow metabolism, we are not talking about metabolic diseases that need to be treated by a doctor. Everything else is the limits of the norm of a healthy person, but with deviations in one direction or the other.
People with a dominant sympathetic nervous system are lucky for those who have been trying to lose weight all their lives. They are slim and have no problems with excess weight.
They are usually lively, active, emotional people, with quick, sharp movements. Their pulse is more frequent, and their blood pressure is increased. They have a more active thyroid gland. They are always a little nervous, excited about life and spend a lot of energy during the day. They don’t get fat, but they also gain muscle with difficulty.
People with a dominant parasympathetic nervous system gain weight easily, and lose weight – with difficulty. These are sedentary, calm, relaxed, and in extreme manifestations — apathetic, sluggish people. They quickly absorb nutrients, which, against the background of a very good appetite, creates problems with excess weight.
In response to excess food, the hypothalamus may not reduce appetite in the following days, as it could be in an ideal situation. One of the metabolic problems is the poor sensitivity of the brain to leptin.
Leptin is a hormone produced by adipose tissue. With its help, the hypothalamus sees the amount of stored energy (fat) in the body. A lot of fat = a lot of leptin. The hypothalamus reduces appetite and increases activity, because there is no need to be afraid of starvation. Little fat = little leptin, so little energy, appetite needs to be increased, and the desire to move – to reduce.
But sometimes the hypothalamus does not see leptin, even if there is a lot of it and fat. And this means constant hunger and decreased activity. A person begins to eat more and more over time.
Sometimes poor sensitivity to leptin is acquired, due to a poor lifestyle and excess weight. And sometimes it is genetic, when a mutation in the structure of the hormone itself or in the receptors of the hypothalamus prevents the signal from being received correctly.
If a person with a slow metabolism suddenly decides to go on a starvation diet, great torment awaits him: his appetite becomes simply brutal. Begins to pull on all the fat, sweet or salty. Activity drops very much and puts him in amoeba mode with constant thoughts about food, bad mood, lack of strength and libido. The work of the thyroid gland worsens even more.
Added to this is the low sensitivity of muscle cells to insulin, which makes fat deposition easier.
From an evolutionary point of view, it was those who could store more fat to survive hunger, long winters and pass on their genes to offspring who survived. Now this is no longer an evolutionary advantage, but many of us carry these genes and struggle with excess weight all our lives.
Change in metabolic rate
Before that, it was about things partly genetic. But man is not a closed system. We are very influenced by the environment. A hundred years ago, metabolism was less dependent on it. But today we have an abundance of food – fatty, sweet, high-calorie, always available. We move less — we have cars, subways, planes, and every technique simplifies life.
Sedentary lifestyle, poor nutrition, stress, lack of sleep – all this knocks down the weight self-regulation system, disrupts eating behavior. The hypothalamus stops correctly perceiving the body’s signals, the muscles lose sensitivity to insulin. In the worst case scenario, a metabolic syndrome develops — type 2 diabetes, hypertension and atherosclerosis, which often go together and reinforce each other.
And if it is difficult to fight genetics, a lot can be done with lifestyle. Even the most hopeless person from the point of view of genetics is capable of big changes.
“Acceleration” of metabolism
Talking about the “acceleration” of metabolism is not correct. Instead, you need to think about how to get it back to normal. Highly accelerated metabolism is a serious disease (for example, Basedova disease).
What reduces metabolism? Sedentary lifestyle, lack of strength training, muscles, passion for sugar and saturated fats, eating disorders. And this is “treated” by a change in lifestyle.
You will lose weight, restore the sensitivity of cells to insulin with the help of diet and strength training, and the metabolism will return to normal as much as possible. You will learn to eat when you are hungry and not to eat when you are full, stop bombarding the brain with endorphins from high-calorie food, improve sensitivity to leptin.